Monday, 28 May 2007

Went down to GD on Friday and got everything on the list apart from the oil cooler (on back order) and the handbrake cable (forgot to check in my box properly!). It was useful to spend a while picking Craig's brain and I came away with plenty of hints and tips. So without more ado here they are:

3 Row Radiator:

Twin Fan Kit:

Pair of used Chevy Headers - I say used but they were only on a car for as long as it took to take to the SVA test and back - the engine was then swapped. I could polish them.... but then they would only yellow again the first time they were used!

A do-it-yourself stainless steel exhaust system!:

I knew the exhaust system was 2.5 inch but didn't expect to find the back boxes had a bigger outlet to fit the 3 inch tail pipes:

Now that's what I call an exhaust! (pint glass for scaling purposes) - you could loose fair size animals down that!

I also partly sorted my body order out - but not quite. I was going to go for RAL3020 - Traffic Red - but Paul and Craig reckoned that would end up looking a bit pink/orange. The reality is that the gel coats come out a shade or two lighter than the swatches. Now good fortune had it that there were some T70 body panels in the shop that I liked and also a MK4 body outside destined for Germany in the same colour - RAL3001 - Signal Red. Now I like the look of this - but when I got back and looked at my photos it seemed a bit pink - probably the camera? - and then depending on how your monitor is set up it'll look different again!!

To make matters worse, Andy had driven back that morning from the Connaught Show in London in a Red T70 - Now I liked that Red as well - forgot to take a photo, and to ask what colour it was!! I'm getting confused - I can see why black is a popular colour!

I had a look at some of the cars in the workshop and there was a nicely trimmed MK3 - although I don't like the blue body / cream interior that a lot of people seem to go for this one was nicely done. I think I'm sold on the diamond stitched tunnel top and rear bulkhead as opposed to carpet - more cost!

What next? Well three weeks until the engine lands but there's quite a few things to do now:

Some stainless steel polishing.

Fabricating a radiator frame to hold the fans (Craig recommended not using the zip-tie-through-the-radiator fixings as supplied by Pacet as they can damage the radiator).

Thursday, 24 May 2007

Off to GD tomorrow - still seems to be a bit of confusion as to what will be ready? The main thing I'm going to need is the gearbox mounting bracket - this will enable me to get the engine and box in. I'll need to go back anyway as I'll have to drop my gearbox yoke off to them to get the propshaft made up.

Whilst I was on the phone to Andy I talked about the Bump Steer measurements I had taken. He confirmed that that the residual bump steer effects I had measured would not be noticeable on the road, plus the slight increase over the last 1/2 inch of droop was nothing to be concerned about - If the car is that unweighted you'd be more worried about which hedge you were just about to go through - were Andy's words. Seems fine to me!

The other reason for going down is to order the body. According to my programme I'm not going to need this for quite a few months. This is mainly down to finances.... I don't want to borrow to fund this project so that means saving up - this is what takes the time!! The body represents a significant investment as I've opted not to do everything myself.....

I have decided to get GD to cut the body holes, remove the flash lines, fill seams, hang doors, fit bonnet and boot and finally finish and polish the gel coat. I have a number of reasons for this.

I have never worked with fibreglass and would prefer to start on something less critical than the body!

I'm going for a gelcoat finish and GD will be able to finish this to a much higher standard than I will be able to achieve - I'm not doubting my abilities just being realistic!

Whilst they are at all this they may as well fit the doors, boot and bonnet and get them fitting properly - It is important that the finished car doesn't look cack handed!

A couple of people that I have talked to and some others on the cobraclub forum have recommended this route after their own experiences.

All this work incurs a fair bit of additional (unbudgeted!) expense - however it is more than justified in my mind in terms of the end result. The additional expense is about 5% of the original build cost, this seems worth it considering the end result - which if GD do it will be guaranteed - but would involve some degree of chance / luck if I was responsible for it all!

The downside obviously is the time delay in order to save up. However Andy estimated that this approach would save around 90 hours of my time. I seem to have been averaging around 12 hours a week in the garage - so this would equate to roughly 8 weeks saved. Now this is more or less the additional delay. So in reality there's no big difference in the overall programme. The only difference will be that I'll have nothing to do for 8 weeks instead of filling the house with fibreglass dust!

So I may have time to knock together a temporary dash and electrics and annoy the neighbours by running the engine?.............

When I get back on Friday I'm straight away again for a long weekend so there'll be no photo's of bits 'till next week.

Saturday, 19 May 2007

Did it all again with the steering rack locked - still the same. Fiddled around with the rack height but still couldn't get it any better.

I also double checked the effect of lateral hub movement and the fact that the laser was at a very slight angle - less than 0.25mm (by calculation) on the measurements on the graph paper.

Double checked my trigonometry - OK

??

Having done a trawl on the Internet it appears to be the case that you can never eliminate bump steer in the majority of cases. The aim of the exercise is to minimise it as much as possible. For a given suspension geometry this becomes increasingly difficult at the extremes of suspension travel.

You have to ask the question if the Jag Suspension was ever designed with zero bump steer in mind? - either way we are kind of stuck with it!

Looking back at the graph you can see that changes in toe-in are minimal for most of the suspension range - only at the extremes does it increase. Let's face it - at full droop (i.e. wheels off the ground!) the last thing on my mind will be bump steer!

The change in camber is interesting and to some extents is intended to cater for the effects of roll when cornering. It is fixed by the geometry of the wishbone pivots and cannot therefore be changed.

Now for the best bit-

Where did the rack end up? -

Within half a gnats tadger of where it was set using the parallel straight edge method!!!!

That's engineers for you!

P.S. Check your ride height toe-in after all this and adjust as necessary. Which reminds me - I need to do mine!

First job was to fix a mirror to the brake disc (used a piece cut off a cheapo mirror from B&Q):Then the laser was set up and the piece of graph paper was fixed conveniently to the garage door about 8 feet away:The results of the first test can be seen in the video below:

There did appear to be some bump steer effect remaining - remember the effect is magnified - firstly the mirror doubles the angle and secondly the plot is being made some 8 feet way from the mirror. You can see that there is a marked increase in bump steer during the last 1/2 inch of droop. I noticed this during the visual check with the two straight edges.

So I spent a bit of time mucking around with the rack position - easy to do - just watch the dot on the wall as you move the rack. I found I could reduce the bump steer effect over the majority of the suspension range but with the exception of the last 1/2 inch of droop. The following video shows the end results of my best efforts:

Still some bump steer effect - but how much?

So taking the points I made on the graph paper I could determine the movement of the laser and with a bit of basic trigonometry relate these measurements back to angular movements at the hub. The following graph shows the results in terms of change in toe-in measured in arc seconds and camber change measured in degrees. Camber change and toe-in change are taken to be zero at the notional ride height of 11.5 inch damper length.

CLICK ON GRPAH FOR BIGGER IMAGE

You can see the marked increase in bump steer effect (green line) over the last 1/2 inch of droop - over the majority of the range there doesn't appear to be a great deal. But how do arc seconds compare to toe in? Lets plot another graph - this time of toe in change of the wheel with relation to damper length:

CLICK ON GRAPH FOR BIGGER IMAGE

So if we forget the last 1/2 inch of bump the effect on toe in is +/- 0.5mm - toe in on bump and toe out on droop. Over the middle range (10.5-12.5 inches on the shock) it's bugger all.

The only thing that has just crossed my mind is that during all this the steering rack was free to move - I wonder if this has affected the results?

Right - back to the garage - lock the rack and see if it makes any difference? - I'll be back shortly.

Friday, 18 May 2007

Bump steer is a phenomenon that occurs when the inner track rod end ball joint does not lie on the plane formed by the upper and lower wishbone inner fulcrums. This means that as the suspension moves the track rod will effectively lengthen/shorten relative to the wishbone pivots thus causing the associated wheel to toe in/out. In practice this means that driving on bumpy roads can cause an undesired steering effect and will make the car feel "twitchy".

I got my replacement track rod ends and set up the front as I had done before - using the method of visual alignment of two straight edges to check the bump steer. This has been the only part of suspension geometry that I've not been able to physically measure.

Now I'm an engineer - I like to measure things - it's in my nature!

So how do you measure bump steer without buying an extremely expensive bump steer gauge?

The answer to this question is not as simple as it would first seem. In order to measure something you need a datum to measure the thing relative to. So that's easy then, just find a datum. Hmmmm.... easier said than done!

There are a number of problems with this.

As the suspension moves from full droop to full bump the ends of the wishbones (and therefore the hub) move in a vertical arc. This means that the hub will move initially away from the chassis and then (after the wishbones have passed the horizontal) towards the chassis. You cannot therefore use a point on the chassis as a reference as the datum would not be constant (remember we are trying to measure small changes).

Due to the unequal length of the wishbones the camber measurement will change as the two wishbones describe different vertical arcs. If you used a point on the wishbone as a datum, any measurement to the hub would be affected by this.

The measurements need to be taken with the suspension at different heights - therefore the system of measurement needs to be independent of change in suspension height.

Now this one has had me puzzled for a few days..... but maybe there is an answer.

We need a datumindependent of the suspension, but also one that is not affected by the position of the suspension.

So then, let us assume we fix a mirror on the brake disc and shine a laser at it. This allows us to use the reflection of the beam to double the angle measured and therefore increase the accuracy of the measurement - it would look something like this viewed in plan:

The above diagram is exaggerated - the angle of the laser needs to be as square to the mirror as possible (just enough to let the reflected beam back past it) otherwise as the hub moves in/out relative to the laser the beam will be deflected and give a false reading. In elevation the only key thing would be that the laser needs to be horizontal:

If there was no camber change and zero bump steer then the angle of the mirror would not change (although its vertical position would as the height of the suspension changes) and the laser dot on the graph paper would therefore not move.

If the camber changes then the laser dot would be deflected upwards or downwards on the graph paper.

If bump steer is present then the toe in/out angle would change and the laser dot would be deflected left or right on the paper.

Taking measurements at different suspension heights would give a number of points on the graph paper which can be joined to form a curve. Any horizontal deflection of this curve would represent a measure of bump steer and any vertical deflection would represent a measure of camber change.

If the distance of the graph paper from the mirror is known, then the measurements on the graph paper can be converted to actual angular measurements.

The further the graph paper is from the mirror then the greater the deflection of the laser beam and therefore the greater the accuracy.

Thinking about it there are two other criteria: the graph paper must be vertical and must be aligned perpendicular to the reflected beam (in order to be able to calculate the angular deviation).

Seems like a cunning plan - so back up on the axle stands - off with the wheels and remove the springs.

I have been speaking Ian Briggs at British American Engines today to sort out a couple of queries. Tonight Ian rang me and made me an offer I couldn't refuse..... I'll spare the details but the upshot is my engine will still be a chevy 383 but in a different flavour......

425BHP and 470ft/lb!

I cannot rate these guys highly enough - If you are after a yank V8 then BAE is the place to go

Tuesday, 15 May 2007

Track rod ends turned up the post today - so that was it - nothing for it then! Rod ends fitted to steering arms - toe in and bump steer set and checked as before (at least it's quicker second time round!) Refitted the front dampers and springs and then the front wheels.

Then it was off the axles stands and onto the floor for the first time!

Saturday, 12 May 2007

Having not much that I am able to do at the moment I occupied a little bit of time by fitting the handbrake caliper return springs. The springs are the standard Jaguar part (not everybody fits them) and fit quite conveniently to the GD chassis. The hooked end of the spring fits snugly over an M5 bolt sandwiched between two washers - a spring washer and a rivet nut complete the installation:

Having finsihed fiddling with my back end????? I put the donor wheels on the back to clear up a bit more space in the garage. Startng to look like it may actually be capable of moving at some point in the future when I get some track rod ends!!

Well, over a week has gone by and I've done....... nothing! I can't believe it's four weeks now I've been waiting for my replacement track rod ends - I'm going to have to get onto GD to see what's happening. Problem is that my engine should be here in 5 weeks and I need to move the chassis to make room to get the engine and box in the garage and to give enough space to get them assembled together. Now it's going to be much easier to move the chassis with the wheels on!

However, I've not been totally inactive. I've spent some time sourcing all the plumbing components for the engine and gearbox installation. But I'm not going to order anything until the engine is in so I can determine the exact lengths of pipe runs and the optimum positioning of the various bits and pieces.

Mind you - one thing I have done is set up a wireless network - at last! First effort took five hours with no luck. Then, following an unpleasant (for the shop assistant!) scene in PC World and a different wireless router - 5 minutes - done! You never know - Cobracam stands a chance of being resurected - this time in the right place!

Wednesday, 2 May 2007

Fixed the fuel pipe into position tonight - glad I've got a 90 degree attachment for my drill - made life a lot easier!

So yet again I'm going to start finding I've got time on my hands - 6 and a bit weeks until my engine arrives with only a few small jobs to do. Time to start sourcing all the parts I'll need for the install.

My track rod ends are expected by GD from their supplier this week - so next week I can set the front end up all over again - should be easier second time around!!

Tuesday, 1 May 2007

Met up with Lee Topham today and picked up his now redundant jag wheels. First Time I've met a fellow Cobra Builder in the flesh! Lee's GD is nearly on the road and is pretty impressive - cleveland motor, narrowed jag rear end for a more realistic dish to the wheels and side pipes! I now feel more enthused than ever! so here they are:

Not much to look - but it will make big difference when they are on - it'll really start to look like a car! All I need now are some track rod ends (still waiting) and some wheels nuts (Doh!). I also got some 10mm P Clips for the fuel line today and after speaking to Craig at GD about fixing positions I think I'll finish the fuel line off tomorrow.